An Active Knee–Ankle–Foot Orthosis With Torque‐Dense, Low‐Impedance Knee Actuation

Passive knee–ankle–foot orthoses (KAFOs) are commonly prescribed for individuals with lower‐limb impairments, but they cannot fully compensate for impaired limb function and often lead to unnatural, slow gait and chronic injuries. Powered exoskeletons are a promising alternative, but existing devices either lack the torque required to support users with severe leg weakness or the speed and backdrivability needed for natural walking and user‐coordinated motion. In this study, we present an active KAFO that addresses this gap by using a torque‐sensitive robotic actuator to power the knee joint. Benchtop experiments show that the proposed actuator (1.45 kg) has high‐peak‐torque capability (113 N m), high‐speed capability (2500°/s), and low impedance (0.75 N m s/rad). Initial testing with an able‐bodied participant demonstrates the active KAFO's ability to deliver biological‐level torque and power. Clinical testing with three participants with lower‐limb impairment suggests that the proposed active KAFO can restore users’ ability to climb and descend stairs step‐over‐step and improve walking performance beyond the capabilities of passive orthoses. These results indicate that the proposed active KAFO may improve mobility for individuals who typically rely on passive orthoses.